Fuel cell systems with integrated humidification are known. Reference is made, for example, to German Patent DE 101 04 246 C1, which describes a fuel cell having two humidification units in which the process gas is humidified with the moisture contained in the exhaust gas, while heat is extracted from the exhaust gas streams by means of one heat exchanger, respectively, said heat being supplied to the process gas to evaporate the water contained therein.
U.S. Pat. No. 6,656,620 B2 also describes the transfer of a quantity of heat, especially from the exhaust gas to the process gas in a humidifier.